Method of fracturing to control wild wells



Oct. 10, 1961 J. Hulr'r ET AL METHOD oF FRACTURING To CONTROL WILD wELLs Filed April 30, 1959 i IIlllllllllllllllllllillItIlltlifllllIIllllllllllllllllllill.

Patented Oct. l0, 1961 ice 3,003,557 METHOD F FRACTURING TO CONTROL WILD WELLS Jimmie L. Huitt, Glenshaw, Pa., and Abraham J. Tepiitz,

San Tome, Venezuela, assignors to Gulf Research &

Development Company, Pittsburgh, Pa., a corporation of Delaware Filed Apr. 30, 1959, Ser. No. 810,095 5 Claims. (Cl. 16o-4t2) This invention relates to a method of controlling an oil or gas well and more particularly to a method of regaining control of an oi-l or gas Well that has blown out.

During the drilling of oil and gas wells, a drilling mud is usually circulated down the drill pipe, through the bit, and up through the annulus between the drill pipe and the borehole wall. One of the functions of the drilling mud is to establish a hydrostatic head opposing the flow of fluids into the borehole from the formations penetrated during the drilling. Sometimes the pressure on the formation is higher than the hydrostatic head exerted by the drilling mud and the formation fluids enter the borehole.

The entrance of formation fluids into the borehole reduces the average density of the column of fluids in the borehole, and hence, the hydrostatic pressure exerted by the fluids in the borehole, which in turn causes increased flow of formation fluids into the borehole. The flow of the formation fluids may get completely out of control to cause a blow-out or wild well. Frequently the oil and gas flowing from a blown out wellbecomes ignited and destroys the drilling rig over the well. The high pressure gas flowing through the borehole may blow through the ground around the casing to cause a crater at the well head into which the drilling rig falls. In addition to the danger and loss of rig resulting from a blow-out, there may be a very large loss of gas and oil. In a recent blow-out, it was estimated that 150,000 barrels of oil a day blew out of the uncontrolled Well.

One of the methods used for regaining control of a wild well is to lower a very heavy open valve over the casing by means of a crane. The valve is locked in place on the casing and then closed. lf the well catches fire it may not be possible to install the heavy valve. If there is leakage around the casing, control of the well cannot be regained by the installation of a valve. It has been the practice when a valve cannot be installed or is ineffective, to drill an offset well in an attempt to intersect the wild well, ordinarily in the formation causing the blow-out, and to ood that formation with fluids pumped down the offset well. The offset wells have been directional wells that are very carefully drilled in an attempt to come within a few feet of the wild well. During the drilling of the offset wells, frequent surveys are made to determine the location of the bottom of the hole to allow corrective measures .to be taken. rIhe drilling of an offset well under such conditions is extremely slow and may require several months if the wild well is a deep well. Thus, the loss resulting from the blow-out is increased by the cost of the drilling rig during a very slow drilling operation, the many surveys required to control the drilling in an attempt to intersect the wild well, and the large loss of gas and oil caused by the delay in bringing the well under control.

This invention resides in a method of gaining control of a wild well in which an offset Well located at a convenient distance from the wild well is rapidly drilled by conventional drilling methods. Only such steps are taken to direct the offset well toward the wild well as will not appreciably slow the drilling. The offset well is drilled to the desired depth and then a substantially horizontal fracture is made from the offset Well to intersect the wild well. A fluid is then pumped down the offset well and through the fracture into the wild well to bring the wild well under control.

The single figure of the drawings is a diagrammatic vertical sectional View illustrating a wild well which has cratered and an offset well drilled to bring the wild well under control by the method of this invention.

Referring to the drawing, a wild well, indicated generally by reference numeral 10, was drilled to a total depth 12 in a high pressure formation -14 when the Well blew out. Casing 16 had been set in the upper par-t of the borehole in accordance with conventional practice. ln the blow-out illustrated in the drawing, gas from the high pressure formation 14 had traveled upwardly around the casing -16 and blown out at the surface to form a crater 18 around the well. Well 10 is illustrated with the well head equipment removed.

In order to bring the Well 10 under control, an offset well, indicated generally by reference numeral 20, is drilled at a safe distance from the wild well 10. lf offset well 20 is relatively close to the wild well 10, yfor example, within about 200 to 400 feet of the wild Well, depending upon the characteristics of the formation to be fractured, it may be a straight vertical well. lf it is necessary to locate the well 20 at a greater distance it may be made to slant towards the wild well or may be a directional well. The offset well 20 illustrated in the drawing has been drilled as a directional well with one change of direction to bring the bottom of the borehole closer to the borehole of the wild well 10. It is an important advantage of this invention that careful control of the location of the bottom of the offset Well 20 is not required as it is only necessary to drill to within about 200 to 40() feet of the borehole of the wild well. The

very rough control of the location of the bottom of the Y offset well in this invention is not such as to require periodic borehole surveys nor slow down the rate of drilling. Whereas a directional well drilled for killing a wild well by the processes heretofore available might require several months to drill to a depth of 10,000 feet, the offset well 20 may, in some formations, be drilled to the same depth in days or less.

Offset well 20 is drilled through formations near the surface and casing 22 is set in accordance with the conventional practice. The drilling is then continued to a total depth 24 in a formation, referred to for identification, as shale 26, above the high pressure formation 14.

After drilling to total depth 24, a horizontal fracture 30 is made in the shale 26 and extended to intersect the borehole of wild well 10. The borehole of well 20 could v be made to extend into the high pressure formation 14 and the fracture 30 connecting the offset well with the wild well made through the high pressure formation 14. lt is often advantageous to make the fracture 30 in a higher fonmation than the high pressure formation to avoid damage to the high pressure formation which might interfere with the later production of oil or gas from the high pressure formation. lt is only necessary that fracture 30 be made below the bot-tom of casing 16. It is preferred, however, that the offset well be drilled to substantially the same total depth as the wild well and the fracture be either in the high pressure formation 14 or immediately above the formation to increase the height of the column of plugging fluid that can be injected into the wild well through the fracture to kill the Wild well.

Horizontal fracture 30 can be made by forming a horizon-tal notch around the borehole wall of well 20 at the desired depth with a reamer orA explosive charges. After the notch has been formed, a borehole packer 32 is set immediately above the notch and tubing 34 is extended through the packe-r to open into the borehole below the packer. If difllculty is encountered in setting a packer, the entire hole can be subjected to the hydratilic pressure used to form and extend the fracture. A frscturing fluid, for example Water, is then delivered into the upper end of tubing 34 from a supply line 36 at a pressure high enough to fracture the formation. A low penetrating fluid such as water containing a gelling or thickening agent is than pumped through tubing 34 and into fracture to extend the fracture until it intersects the borehole of wild well 1G. Examples of low penetrating liquids that can be used are dispersions in water of natural gums such as karaya, batu, or Guar gum. Oil base fracturing fluids such as diesel or crude oil containing napalm type soaps are also suitable for extending the fracture. it is advantageous to add to the liquid used to extend the fracture an additive designed to reduce the fluid loss into the formation. Many such additives are commercially available. The method of orienting and forming a horizontal fracture in a Well is described in our application Serial No. 721,286 tiled March 13, 1958, entitled Method of Fracturing Earth Formations Penetrated by a Well.

After the fracture has been formed, a liquid is pumped through tubing 34 and fracture 30 into the borehole of the wild well 10 to form a column of liquid in the boreu hole of that well which will prevent flow of formation fluids into 4the well. A suitable liquid is a high density aqueous liquid having a density higher than' about 10 pounds per gallon, and preferably 14 pounds per gallon or higher. Examples of suitable liquids are water having finely divided barium sulfate, lead sulfide, or iron oxide suspended in it. The high density liquid delivered through fracture 3Q into the borehole of wild well 1) forms a liquid column therein which exerts a hydrostatic pressure high enough to stop the flow of formation fluids into the borehole. High density slurries of cement also `may be pumped through the fracture and into the borchole of well 1i) to kill the Well.

A particular-lu useful material for pumping into the well itl is one having negative thixotropic properties. Such liquids when vigorously agitated become highly viscous. The high turbulence in the wild well will cause the liquids having negative thixotropic properties to form a stid mass which interferes with the rapid flow of the formation fluids through the borehole. The' negative thixotropic liquids may be followed with high density liquids of the type described above to build up a column of high density liquid in the borehole. Liquids which' have negative thixotropic properties and which can be used are dispersions of acrylic resins in suitable solvents. Examples of suitable liquids of negative thixotropy are polyacrylic esters such as the polyacrylates, polymethaorylates and polyethacrylates. They may be dissolved in volatile liquid hydrocarbons. A preferred negative thixctropic solution is a 5 to 10 percent solution in water of polymethacrylic acid of degree of polymerization of 10,000. A 5 percent aqueous solution of that po-lymethacrylic acid will increase in viscosity from 5 poises to 1,750 poises on being subjected to rate of shear of -1 secends. The nega-tive thixotropic liquid can also be used as a low penetrating liquid to extend the fracture.

This invention provides a method for bringing a Wild Well under control without the delays inherent in the drilling of odset wells to within a few feet of the borehole of the wild well in the manner previously employed for killing wild wells. Athough drilling the odset well to come close to the borehole of the wild well is not a disadvantage to the method of this invention, only by chance could an offset well be drilled to locate its bottom close to, for example -within 25 feet of, the borehole of the wild well `without repeated borehole surveys and slow and careful directional drilling. With this invention, the odset well may be drilled rapidly, -it being easy to drill the borehole to Within about 2G() feet of the Wild well without delaying the drilling from normal schedules. By

making a substantially horizontally oriented fracture from the odset well, intersection of the fracture with the borehole of the wild well is assured.

We claim:

l. A method of killing a wild well comprising drilling an odset well adjacent to thc wild well and to substantially the same total depth as the wild well7 cutting a notch in the borehole wall of the offset well for the initiation of a substantially horizontal fracture, forming a substantially horizontal fracture extending from the odset well, displacing u low penetration liquid into the fracture to extend the Ifracture to intersect the wild well. and displacing a liquid down the offset wel] and through the fracture into the wild well to kill the wild Well.

2. A method of killing a Wild well comprising drilling an odset well adjacent to the Wild Well to a total depth substantially the same asV the total depth of the wild well, the bottom of the odset well being within about 400 feet of the bottom of the wild well, cutting a notch in the Wall of the borehole of the odset well near the bottom there of for initiating a horizontal fracture, pumping water down the odset well to form a horizontal 'fracture extending from the odset well at the notch in the borehole wall, pumping a low penetration liquid down the offset well to extend the fracture to intersect the wild well, and pumping a liquid down the odset well through the fracture and into the borehole of the wild well to kill the wild well.

3. A method of killing a wild well penetrating a high pressure formation from which formation fluids enter the borehole of the wild well to blow fluids therefrom comprising drilling an odset well to a formation above the high pressure formation from which the fluids enter the wild well, said odset well being spaced at its lower end within about 400` feet of the wild well, cutting a notch in the wall of the borehole of the odset well near bottom thereof to initiate a substantially horizontal fracture in a formation above the high pressure formation, pumping a. liquid down the odset well to fracture the formation at the notch formed in the borehole wall, extending the fracture to intersect the wild well, and pumping a high density liquid down the offset well and through the fracture into the wild well to kill the wild Well.

4. A method of killing a wild well penetrating a high pressure formation comprising drilling an odset well adjacent to the wild well and into a formation above the high pressure formation, the bottom of the odset well being within about 25 to 400 feet of the borehole of the wild well, cutting a substantially horizontal notch in the borehole Wall of the odset well near the bottom thereof, pumping a liquid into the odset well to initiate a substantially horizontal fracture at the notch, pumping a low penetration liquid down the odset Well to extend the fracture to intersect the wild well, and pumping 'a high density liquid down the odset well and through the fracture into the wild well to kill the wild well.

5. A method of killing a wild well penetrating a high pressure formation comprising drilling an odset well adjacent to the wild well and into a formation above the high pressure formation, the bottom of the odset well being within about 25 to 400 feet of the borehole of the wild well, cutting a substantially horizontal notch in the borehole wall of the odset well near the bottom thereof, pumping a liquid into the odset well to initiate a substantially horizontal fracture at the notch, pumping a low penertationl liquid down the odset well to extend the fracture to intersect the wild well, and pumping a nega'- tively thixotropic liquid down the odset well and through the fracture into the wild well to kill the wild well.

(References on following page) 5 6 References Cited in the file of this patent OTHER REFERENCES E UNITED STATES PATENTS The Petroleum Handbook, 3rd editi on, 1948, The 2,766,828 Rachford Oct 16, 1955 Shell Petroleum C0., Ltd., page 100 felled 011- (Cpy 2,880,587 Hendfix et a1. Apr. 7, 1959 5 m Dwso 49) 

